The present invention relates to a method for drying a nonionic alkylene oxide-type water-soluble resin, and to a nonionic alkylene oxide-type water-soluble resin dried according to the method. The invention also relates to a method for packaging the resin and to a packaging material for it. The invention further relates to a method for transporting a nonionic alkylene oxide-type water-soluble resin
For obtaining resin of high purity and good processability on an industrial scale, heretofore generally employed is (1) a method of precipitating a polymer by the use of a bad solvent after solution polymerization to produce it, then separating it through filtration or centrifugation, and drying it into powder; or (2) a method of separating a polymer through filtration or centrifugation after precipitation polymerization to produce it, followed by drying the resulting into powder, and finally, the thus-dried and pelletized or powdered resin is stocked for a material for various applications.
Nonionic alkylene oxide-type water-soluble resin such as ethylene oxide-type resin (e.g., see Herman F. Mark, Norbert M. Bikales, Charles G. Overberger, George Menges, Encyclopedia of Polymer Science and Engineering, Vol. 6, USA, Wiley Interscience, 1986, pp. 225–322) is used for various applications these days. In particular, ethylene oxide-butylene oxide copolymer (hereinafter it may be referred to as EO-BO copolymer) resin has a possibility of expressing excellent electrochemical characteristics, and its usefulness is specifically noticed as a material for electrochemical devices such as cells.
However, powder and pellets of nonionic alkylene oxide-type water-soluble resin rapidly absorb water in the environment, and when left in an ordinary environment, they may absorb water to have a water content of from thousands to tens of thousands ppm within about 10 minutes. Since the organic solvent and water in the resin may have close relation to the physical properties and the electric properties of the resin, it is an important theme to reduce them.
For drying resin, for example, employed is a method of introducing dry air into a pelletized or powdery resin product stored in a storehouse, as in JP-A7-316223. However, the method is problematic in that it is difficult to uniformly and entirely dry the resin product within a short period of time according to the method and the drying efficiency of the method is low.
JP-A 2002-1727 proposes a method comprising jetting a hot gas into a store tank of resin pellets, keeping them static in the condition for a predetermined period of time, then taken out the pellets from the store tank, and thereafter again returning them into the store tank, and the method is repeated for drying the resin pellets. In the hot air drying method, air does not contain an organic solvent. Therefore, the method is suitable for removing an organic solvent such as heptane to dry resin.
However, when water is removed according to the method, it is difficult to dry the resin so as to make it have a water content of at most 1% (thousands ppm) since air contains water. In particular, it is extremely difficult to reduce the water content of the dried resin to at most hundreds ppm. In addition, the step of taking the pellets out of the store tank, again returning them to it, and repeating this operation has another problem in that it requires a large-scale apparatus since a condition that the resin is kept out of contact with air during the treatment is indispensable to the step. Even when dry hot air is used, an amount of the air of, for example, at least 100 m3/hr/t and a long drying time are necessary (e.g., see JP-A2002-1727). In particular, since water-soluble resin has good affinity to water, its drying time is further longer.
Hot air could not be applied to powder and pellets of low-melting-point resin since it melts and fuses the resin. In such a case, the resin must be dried according to a specific method of, for example, keeping it in an absolute dry condition in which its dew point is −80° C. or lower, for from a few days to a few weeks.
The present invention has been made in consideration of the above, and it is to provide a method of easily and efficiently drying a nonionic alkylene oxide-type water-soluble resin so as to make it have a reduced water content within a short period of time, and to provide a nonionic alkylene oxide-type water-soluble resin dried according to the method. Another object of the invention is to provide a drying method capable of being attained even at low temperatures and applicable to a nonionic alkylene oxide-type water-soluble resin having a low melting point, and to provide a nonionic alkylene oxide-type water-soluble resin dried according to the method.
For the dried resin, it is an important theme to keep its dry condition.
For packaging the dried nonionic alkylene oxide-type water-soluble resin with its low water content kept as such, generally employed is a method of substituting gas inside a packaging container.
For gas substitution, for example, there is a method of providing a room (substitution chamber) filled with an inert gas and attaining the intended gas substitution in the chamber. Another method is known, which comprises forming a nozzle hole in the temporarily adhered cap of a container, introducing an inert gas into the container through it, and sealing up the hole after the nozzle has been removed (JP-A 8-192821).
In the former method where the gas substitution is attained in the gas substitution chamber, an empty container may be previously put in the gas substitution chamber, then air is sucked away from the substitution chamber so that the chamber is kept in vacuum, and thereafter an inert gas maybe introduced into the chamber for gas substitution therein, whereby the empty container may also undergo the same gas substitution. In the method, however, every time when the gas-substituted empty container is taken out and another empty gas to undergo gas substitution is newly put into the gas substitution chamber, the entire gas substitution chamber must be treated for gas removal from it to be in vacuum followed by inert gas introduction into it, but this is uneconomical. In addition, the treatment requires complicated equipment and the equipment cost increases.
In the latter method where an inert gas is introduced into an empty container through its body or through its cap for gas substitution in the container, the container is limited to a box. In this, in addition, a specific mouth for gas introduction nozzle insertion is necessary, and the shape of the container is limited. Accordingly, the method is problematic in that it could not apply to various containers of different shapes.
Apart from the above-mentioned gas substitution method, there is also known a method of adding an oxygen scavenger and/or a moisture remover to the filler to a container or fixing it on the inner side of an container so that it may adsorb and fix water and oxygen in the container. In this method, however, the product in the container may be contaminated with the oxygen scavenger and/or the moisture remover as an impurity, and when the container is opened to use the product therein, close attention must be paid to it.
The invention has been made in consideration of the above, and it is to provide a method of packaging a nonionic alkylene oxide-type water-soluble resin in a low water content condition, not troubled by the problems mentioned above, and to provide a packaging material for it.
Another object of the invention is to provide a method of transporting a nonionic alkylene oxide-type water-soluble resin.
When a material resin is used for some purposes or when it is imported or exported or commercially sold, it is frequently transported by some transportation systems. The transportation systems and methods may often have significant influences on the quality of the material resin being transported.
In particular, nonionic alkylene oxide-type water-soluble resin is a resin having an ether bond in the backbone chain thereof, and its characteristic is that its chemical structure is extremely weak to heat. Therefore, when the resin is transported by ship, it is exposed to high temperatures including its store tanks during the transportation process and the shipping characteristic has a significant influence on the resin being shipped, or that is, it produces a problem in that the dried and powdered material resin is fused while being transported by ship, and the processability of the transported resin becomes extremely bad.
To solve the problem, the dried and powdered resin material is once dissolved in a solvent, and the resulting solution is transported. However, this is problematic in that the resin solution will have to be again dried and powdered after its transportation in some cases, and, in addition, for reducing the viscosity of the resin solution, a relatively large amount of the solvent corresponding to it will be necessary in order that a relatively stable solution condition of the resin could be ensured. Accordingly, there may be a probability that some legal controls in point of handling of powerful chemicals, explosives and combustibles must be imposed on the transportation of the resin solution. Naturally, since the resin is once formed into its solution, the method requires a prolonged working time and causes the increase in the production costs.
In any method mentioned above, in general, a packaged material resin is dealt with when it is actually loaded on or unloaded from a transportation system. However, when an overall volume of the resin material for transportation increases, then there occurs still another problem in that the loading and unloading operation takes an extremely great deal of labor and time.
Accordingly, still another object of the invention is to provide a method for transporting a nonionic alkylene oxide-type water-soluble resin, of which the advantages are that the excellent handlability of the resin is kept as such, not detracting from the quality of the resin, the transportation is conveniently and safely attained, the working time is shortened, the transportation cost is reduced and the labor for transportation is also reduced.